Project Summary Post-traumatic stress disorder (PTSD) is twice as prevalent in females as in males, with a proportion of individuals also developing an alcohol use disorder (AUD). Using predator odor stress (PS) as an animal model of PTSD, we determined that two PS exposures significantly increased anxiety-related behavior and neuronal activation in the hippocampus (HC) of male and female C57BL/6J (B6) mice. Notably, intermittent PS significantly increased alcohol (ethanol) intake by 60% (males) and 71% (females), with heterogeneity in the response. Further, ?sensitivity? to PS-enhanced ethanol intake conferred significantly greater corticotropin releasing factor receptor-1 (CRFR1) protein levels in female versus male HC, consistent with evidence for sex differences in CRFR1 signaling following stress. The proposed studies build on the above evidence by testing the hypothesis that comorbidity of PTSD and AUD is due to increased CRFR1 expression in HC neurons projecting to mPFC and that sex differences in CRFR1 induction by PS contribute to this comorbidity. Aim 1 will determine whether sex differences exist in the association between PS-enhanced ethanol drinking and alteration in anxiety, heart rate (HR), and/or compulsive ethanol drinking in B6 mice. We predict that PS-enhanced drinking in ?sensitive? mice will be associated with an increase in anxiety, HR, and compulsive drinking and that there will be sex differences in the pattern of changes. Aim 2 will map changes in CRFR1 expression and neuronal activation by PS and by PS-enhanced drinking in crfr1-gfp mice. We predict that there will be sex differences in brain regional CRFR1-colabelled activity patterns in response to intermittent PS and in the relationship with ethanol intake. Aim 3 will manipulate the activity of CRFR1- expressing neurons using chemogenetic or pharmacologic approaches and determine the impact on PS- enhanced drinking. Two studies will use Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) in crfr1-cre mice to test the necessity and sufficiency of CRFR1 in ventral CA1, with inhibitory (Gi) and excitatory (Gq) DREADDs, respectively. We predict that preventing PS-induced activation of ventral CA1 (Gi DREADD) will block PS-enhanced drinking only in ?sensitive? mice, whereas activating the ventral CA1 (Gq DREADD) will enhance ethanol intake in mice drinking ethanol without intermittent PS. A complementary study will determine whether systemic administration of a CRFR1 antagonist will reduce PS-enhanced drinking intake in B6 mice, with the prediction that the antagonist will be most effective in ?sensitive? mice. Aim 4 will determine whether manipulation of the projection from ventral CA1 to mPFC is important for PS-enhanced drinking in B6 mice, by injecting Gi DREADDs into ventral CA1 and clozapine-N-oxide into mPFC. We predict that preventing PS-induced activation of the ventral CA1 to mPFC projection will block PS-enhanced drinking. Collectively, the information will elucidate sex differences in mechanisms underlying sensitivity to PS- enhanced drinking that can be targeted for the treatment of PTSD-induced AUD.